GSHP vs. Wood Boiler

[DBoon]

In late 2016 or early 2017, my wife and I will be beginning the renovation of a 1926 Arts & Crafts Bungalow, ~1800 square feet. We still have a lot of decisions to make and plans to draw up, but BTU/hr heat loss will be in the 18 to 25k BTU/hr, depending on the choices we make.

We will have a wood stove (don't want to discuss that choice in this post) and we already have a Fujitsu RLS2H mini-split that has quite nicely provided heat to the unoccupied home for three winters now, powered mainly by our 5.4 kWh solar PV array. We'll keep that as well for supplemental heating and summer cooling. But the main source for distributed heat will be hydronic through cast iron radiators suitably sized for spring/fall BTU/hour output using 110 degree supply water.

Initially, my thought was to to install a Frohling wood boiler. As I think more about this and the specialization of the install and operation (for my wife, should I not be around any longer), and the need for some type of backup anyways, I question the suitability. Instead, I am leaning towards a WaterFurnace ground-source heat pump with vertical well bores for loops (necessary in our cold climate). Newer units (5 Series OptiHeat) have higher output temperatures (up to 140 -150 degrees F) with reasonable COPs, making them suitable for deep winter use as well. A 3 ton unit would fit our needs nicely, and could be augmented by the Fujitsu mini-split and/or the wood stove as needed, or rested while we burned wood during the depths of winter (until we decided we were too old to do this anymore).

I am interested in any comments on this.

 

[begreen]

@webfish can give you some background on GSHP. He is in Minnesota where it is known to get just a little cold. Augmented with a woodstove would be my choice. Simpler operation and a nice back up that can be enjoyed for deeper bone warming heat, power outage warmth and a nice fire view.

 

[velvetfoot]

How well does the mini split keep up now? How about just adding another one if it doesn't.
The PV is helping with electric costs.
Its a relatively small place, and it sounds like you're insulating it well in your renovation.
Your wood stove should heat the place by itself. Maybe a heat pump water heater for dhw.

What's there now for central heat? The way I read it,, you were going to add everything.

Adding hot water distribution as well as a boiler, geo or froling, will be a lot of money.

 

[DBoon]

The mini split was installed in order to heat an unoccupied, poorly insulated residence to ~55 degrees in the winter It does what it is supposed to do - soaks up the solar PV array output (for now) and keeps the heating load off an old, antiquated oil-fired furnace that is going to get retired as part of the remodel. I don't need or want a second one - one is good for summer cooling, and it's not realistic to heat all parts of the house with multiple mini-splits and not generate "complaints" or cold spots. Ducted air heating will be replaced with hydronic due to allergies.

So, it's been well thought through. Money is not an issue, and it will be hydronic with cast iron radiators one way or another.

 

[velvetfoot]

Is there a lot of water to water geo thermal in the US? I thought it was mostly water to air.

 

[DBoon]

I don't know how it breaks down water to water vs. water to air - I would believe that water to air is a lot more popular. I would not have considered a water to water GSHP a year ago based on what I knew then to be the very low (120 degree F or less) max output temperatures. This new unit starts to fit better with my needs, so I am reconsidering. I could potentially duct some cooling coils into an HRV/ERV return as well.

 

[Highbeam]

As to the post title. Don't waste your time with a wood boiler. VERY expensive to properly install with all the storage and piping plus you still have a once a day fire to light. I have an 1800 SF shop with tubes in the floor that would be heated by a wood boiler if they made sense. Instead I use good insulation and a woodstove. Use some sort of conventional heat source for your radiators, even resistance electric is surprisingly cheap if your energy costs are like ours. This conventional heat source will be easy to operate by you, your wife, or anybody else whether you are at home or away.

Your minisplit will do the majority of the work anyways when the woodstove is cold.

Ducted air heating will be replaced with hydronic due to allergies.

Odd. I know that forced air can disturb settled dust but they are blowing clean, filtered air. I have seen dirty filters and know that they collect a lot of junk from the air which I thought would be better for allergies. I too suffer from dust allergies and this year we have replaced all carpet in the house with hard surfaces. That alone made a big difference.

 

[Highbeam]

Is there a lot of water to water geo thermal in the US? I thought it was mostly water to air.

There's not a lot of geothermal in the US period. Going to be a whole lot less as air source heat pumps continue evolving to make full output at such extremely low temperatures. Currently down to 5 degrees F which means ALL temperatures in my climate.

The sore spot for me is that these air source heat pumps are all being designed and marketed to the US to heat air and not water for hot water heat. The efficiency drops when they are expected to heat water to 150 or higher as is traditional with old hot water heat designs. No big deal, as DBOON, design your system to use 110 degree water and give us the air source water heaters please.

 

[georgepds]

I second highbeam's opinion of wood boilers. Spend a little time in the wood boiler section of the forum reading about the problems, and quantity of wood these devices use

I have a co-worker who uses one.. he goes through 16 chords of wood a year. I live roughly nearby and go through 2 chords/year with my interior wood stove. Oh yeah.. and when the power fails.. the wood stove still works.. a concern fro some of us

 

[begreen]

PM webfish about his system for some real world numbers.

 

[iamlucky13]

When I've looked up information on ground source heat pumps for a hoped for future house project, the economics look really tough to justify. I'm hearing figures in the ballpark of $30-40,000 for horizontal loop systems - or roughly 3 times the cost of an air source heat pump for about 2/3 the energy use.

I haven't crunched detailed numbers on payback, but at a glance, it doesn't look particularly favorable to me. The possible saving grace is that air source heat pumps are supposed to have 10-15 year life expectancies, where as GSHP's should be 20+.

I'd love to find out I'm mistaken on this, however, and I'm sure GSHP's economics look better if you're in a 7000+ heating degree day climate than where I am, which is a 4500 HDD climate. I see a lot of articles arguing one way or the other, and where the truth lies is not clear to me yet.

Of course, I'm basing my comments on being able to find an ASHP designed to heat water for your radiators. I know they're available in Europe. I'm not sure about here.

I know you said money is no object, but at a minimum, I'm sure low cost is at least a preference, and an air source heat pump would leave more money for other improvements - more insulation, more solar, etc.

If you can get to 18,000 BTU/hour without having to shrink your windows and/or bump your walls significantly into your living space to make room for more insulation, I'd really try to make that happen. That means not only less energy use on a recurring basis, but lower up-front costs, and for a vertical well GSHP, I imagine that half ton reduction in demand could be a couple thousand dollars in capital cost savings to offset the insulation cost.

As for energy, as a really rough estimate, I'd guess cutting 6000 BTU/hour from your design heat loss (probably something more like half that on average over the course of the heating season) would let you get by with 500 to 1000 Watts less solar panels while still zeroing out your power bill on an annual basis.

 

[Circus]

Though cast iron radiators may be quaint they're designed for >180water. 140water will only give half the heat.

 

[Willman]

Go with TRV controlled low water temperature panel radiators. forget the cast iron.Panel rads can provide usable heat from low temp water.Then go with water over air source heat pump. Place in Canada that manufactures control panel for heat exchange, can't remember their name.

Check out Jaga panel rads for more info. A lot less money then groundsource with central distribution to any part of the house via 1/2'' pex tubing.

 

[sloeffle]

We have a Waterfurnace Envision / 5 series GHSP. It is a water - air unit though. We paid no where near some the of the numbers that are being put out for installation costs. We paid a few thousand more than what an ASHP / propane furnace would of cost. We have had it for 3 or 4 years now.

I really like the unit, and if I had to do it over I would purchase it again. The unit really shines in the summer time. You can't beat the 52F degree air that it puts out. During the summer we see no increase in our electric bill.

It does fine in the winter when temps are above 10F. Our electric bill jumps roughly $50 - $75 during the summer. When temps get really cold, we use our wood burning furnace exclusively. If I was in a heating dominated climate, I would opt for mini-split or ASHP / propane combo furnace along with supplemental heat from a wood or pellet stove.

 

[webfish]

I just replaced our Geothermal unit after 18 years. It is a GEocomfort closed vertical loop but is the dual unit hydronic and forced air. It replaced my Econar dual unit , which the compressor had gone bad. It also has the electric auxillary internal unit .

We chose the geothermal because of the original cost of paying the 1/4 mile cost to get NG run to the house 18 years ago and I didn't want to do propane. Most utility companies and states at that time were running very good rebates for putting units in. I don't have my original costs as it was done as part of house budget . I might be able to find it at a later date.

House is 3600 sq feet. The basement I put in the Wirsbo myself and covered probably 1300 sqft. Since dual system forced air heats and cools the rest.

At the time we did it the utility gave discounted electric on a separate meter if you had a 2nd source of heat. They allowed our ZC fireplace so I have always had reduced electric bills and 2nd meter on the geo system.

The replacement cost was about $19k but we get $6000 tax credit ( residential energy credit IRS form 5695)back and we also got $1600 rebate back from utility which was $400 for every ton of the unit. That does include new water storage tank but of course we used the existing vertical loop, duct work and wirsbo.

As far as ROI on the unit I have not run any numbers but I probably will for next year as my plan is to take out the ZC fireplace and add a freestanding wood stove. I don't think the roi is near what they advertised but I was limited on choices but a few things I really like and some I don't

Pros :
No outside air conditioning unit or slab to put it on.
When running air conditioning get free heat for hot water heater.
No fear of carbon monoxide. ( that changes as soon as wood stove put in)
New unit has variable speed compressor so more efficient and quieter.
Love the in floor heat in basement. No cold floors.

Cons:
Forced air that comes out is cooler to feel, where as NG is a hot air feel.
-10 F temperatures when aux electric kicks on spikes the cost. It struggles to keep up when we have 4 hour controlled outages . ( this is why we get cheaper electric though) Also why we are going to add the wood stove. Over 18 years only handful of times but enough that I want to change to have that wood stove in case of longer power outages.

I would do it again but would have done a wood stove since the start.

Our installer is local and he says he is still installing a few a year.

I was told to do the vertical loops vs horizontal even though I had room for horizontal. Installer said they work better.
Don't oversize your unit. Bigger is not better as it turns on and off more often and takes a toll on the compressor.
My original was a completely closed system. New one has access to the water/glycol and local installer said he has less calls on ones that have this feature vs completely closed.

 

[velvetfoot]

Then go with water over air source heat pump.

What is that?

 

[Circus]

go with water over air source heat pump

What is that?

Water instead of air source. It's warmer.

 

[DBoon]

Don't waste your time with a wood boiler. VERY expensive to properly install with all the storage and piping plus you still have a once a day fire to light...Use some sort of conventional heat source for your radiators, even resistance electric is surprisingly cheap if your energy costs are like ours. This conventional heat source will be easy to operate by you, your wife, or anybody else whether you are at home or away.

Hi Highbeam, well, that's where I am basically heading. If I was 20 years younger, I would go with the boiler. Realistically, the wife wouldn't do the work for it if something happened to me, and I am pragmatic enough to at least think about that possibility. And I can't count on a mini split as backup, even one rated to -17 degrees F, in a cold, Central NY winter.

I second highbeam's opinion of wood boilers. Spend a little time in the wood boiler section of the forum reading about the problems, and quantity of wood these devices use

Hi georgepds, the boiler under consideration would be a lambda-controlled indoor boiler, not an outdoor boiler. I am quite familiar with the pros and cons of each,
having spent some time in the Boiler Room for the last 5 years.

Though cast iron radiators may be quaint they're designed for >180water. 140water will only give half the heat.

Hi Circus, it is a historic home remodel, and the radiators will be historically appropriate. We have cast iron radiators in the village house we live in now, and we like the even, sustained heat the provide. They can be sized for any temperature water, provided there is willingness to pay the price (I am, and it is not unreasonable, in my opinion).

Go with TRV controlled low water temperature panel radiators.

Hi Willman, yes, they will definitely be TRV controlled. Already decided, no matter what system we choose to heat the water.

We have a Waterfurnace Envision / 5 series GHSP...It does fine in the winter when temps are above 10F.

Hi Sloeffle, the Waterfurnace products are what I am looking at, but water (not air) output. Do you have horizontal loops, and if so, is that why you feel that you don't have enough heat in the depths of winter <10F, or does it just not have enough capacity for your house?

 

[DBoon]

The replacement cost was about $19k but we get $6000 tax credit ( residential energy credit IRS form 5695)back and we also got $1600 rebate back from utility which was $400 for every ton of the unit. That does include new water storage tank but of course we used the existing vertical loop, duct work and wirsbo.

Hi webfish, your name kept coming up, so I'm glad you replied. Do you remember what your cost was the vertical bore holes and how much vertical feet of borehole did you need? I've read about ~150-250 feet per ton of capacity, and I would probably just get a 3 ton unit. Soils around where I live are glacial till, and shale underneath, so not so tough to get through.

I was told to do the vertical loops vs horizontal even though I had room for horizontal. Installer said they work better. Don't oversize your unit. Bigger is not better as it turns on and off more often and takes a toll on the compressor.
My original was a completely closed system. New one has access to the water/glycol and local installer said he has less calls on ones that have this feature vs completely closed.

One of the primary reasons I'm seriously thinking of the GSHP is that I want to also use it as a thermal battery to absorb excess capacity from my solar PV array, which will probably be expanded in the future as well. My goal is 100% renewable power (net zero) for the house, and I'm looking forward to a time when NY state's net metering laws may be changed from the very nice policies we have today. A 3 ton unit could potentially feed a 500-700 gallon storage tank, and heat the house for 12 hours on the coldest day with enough accumulation of heat energy during the daytime. With any luck, I might be able to take advantage of future load shaving or off-peak demand incentives as well.

Could you describe the difference again between your original completely closed system and the one you have today?

 

[DBoon]

I know you said money is no object, but at a minimum, I'm sure low cost is at least a preference, and an air source heat pump would leave more money for other improvements - more insulation, more solar, etc.

If you can get to 18,000 BTU/hour without having to shrink your windows and/or bump your walls significantly into your living space to make room for more insulation, I'd really try to make that happen. That means not only less energy use on a recurring basis, but lower up-front costs, and for a vertical well GSHP, I imagine that half ton reduction in demand could be a couple thousand dollars in capital cost savings to offset the insulation cost.

Hi iamluck13, I'm still in the process of finalizing construction plans, but I certainly understand the economics of cutting heat loss with better detailing, materials, etc. If I can get to 18,000 BTU/hour, I will certainly do that, since overall the economics mostly pencil out well, and the reality is also that lower heat loss = a more resilient structure in case something goes very wrong. Windows are one of the areas where the heat loss can be massively impacted - but this is a pretty big investment as well for historically accurate and high R (e.g., R-5) center of glass windows with good frames (i.e., not cheap vinyl replacements that will need replacement in 15 years). I think I will probably be at a 3 ton unit in any case since I want to thermally store heat, and there is a minimum size before units don't get any smaller, or they don't make heat fast enough to optimize the BTU/hour necessary to run for 6 hours at maximum output to utilize peak solar PV power.

 

[DBoon]

Odd. I know that forced air can disturb settled dust but they are blowing clean, filtered air. I have seen dirty filters and know that they collect a lot of junk from the air which I thought would be better for allergies. I too suffer from dust allergies and this year we have replaced all carpet in the house with hard surfaces. That alone made a big difference.

Hi Highbeam, after having dealt with forced air, dirty filters, electrostatic precipitators, etc. for nearly my entire adult life, I can't begin to describe the allergy relief I have from having wood floors and hydronic heat. I will never again go back to carpet and non-hydronic heat. Wood floors may be the biggest part of it, but our house with hydronic seems to have a lot less dust on surfaces as well.

 

[webfish]

Hi webfish, your name kept coming up, so I'm glad you replied. Do you remember what your cost was the vertical bore holes and how much vertical feet of borehole did you need? I've read about ~150-250 feet per ton of capacity, and I would probably just get a 3 ton unit. Soils around where I live are glacial till, and shale underneath, so not so tough to get through.


One of the primary reasons I'm seriously thinking of the GSHP is that I want to also use it as a thermal battery to absorb excess capacity from my solar PV array, which will probably be expanded in the future as well. My goal is 100% renewable power (net zero) for the house, and I'm looking forward to a time when NY state's net metering laws may be changed from the very nice policies we have today. A 3 ton unit could potentially feed a 500-700 gallon storage tank, and heat the house for 12 hours on the coldest day with enough accumulation of heat energy during the daytime. With any luck, I might be able to take advantage of future load shaving or off-peak demand incentives as well.

Could you describe the difference again between your original completely closed system and the one you have today?

I know I had 4 vertical loops but do not recall the depth. I know I was at work when they installed and did it in a day.

My system is still closed on the new one but the flow center is open and just the column of water is enough pressure for the pump. My old system was pressurized and closed. Just a comment from my tech who has seen hundreds of installs and he has had less issues with the non-pressurized. Makes it easy to see if any fluctuation in the water level too.

My unit is 4 ton and does 3600 sq ft. Basement in floor and the rest forced air. Below 10 degrees it can do it on its own but I would not without the auxilllary internal electric. Long stretches below 0 can become costly.

 

[sloeffle]

Hi Sloeffle, the Waterfurnace products are what I am looking at, but water (not air) output. Do you have horizontal loops, and if so, is that why you feel that you don't have enough heat in the depths of winter <10F, or does it just not have enough capacity for your house?

Yes, we have horizontal loops. One loop is buried at 4' and the other is buried at 6'. We have a 4 ton unit and have 2400' feet of pipe in the ground. Our installer installs 600' of pipe per ton of furnace capacity. I had other installers only want to install 150' of pipe per ton. Make sure your installer provides you a geolink report.

Our unit was designed to keep the house at 70F without resistance heat until 0F. It has no problems doing that but would probably run 18 hours a day. It would cost roughly $5.83 a day to run it during those really cold days. My German frugality cannot bear to see that money spent so I choose to burn wood instead. I have thousands of dead ash trees in my woods that need cut down and burned anyways.

I would also recommend getting an Intellistart for your geo. It will make buying a generator a lot cheaper sinces it take less LRA to start the unit. It can be ordered to come from that factory with one. Make sure you installer doesn't add it on later. It has a much better warranty if it is installed at the factory. You will probably need that anyways if you plan on going off grid.

My second recommendation is to hook the DSH on the geo up to the cheapest 80 gallon hot water tank ( think of that as a battery ) you can buy and then buy a HPHW to make hot water when your geo isn't running.

 

[maple1]

I second highbeam's opinion of wood boilers. Spend a little time in the wood boiler section of the forum reading about the problems, and quantity of wood these devices use

I have a co-worker who uses one.. he goes through 16 chords of wood a year. I live roughly nearby and go through 2 chords/year with my interior wood stove. Oh yeah.. and when the power fails.. the wood stove still works.. a concern fro some of us

Wood boiler here. 5 cords per year, no problems. I can also heat with it when the power goes out.

 

[DBoon]

My system is still closed on the new one but the flow center is open and just the column of water is enough pressure for the pump. My old system was pressurized and closed.

I think I get it - it is filled the same way, but one is under pressure and the other is not.

My unit is 4 ton and does 3600 sq ft. Basement in floor and the rest forced air.

What infloor/underfloor hydronic system do you have? It would be quite easy for me to add this under the 1st floor subfloor and wood floors (1-1/2" of pine and fir), and I like the idea of bleeding off <110 deg F heat in the underfloor to give me more thermal battery capacity for heating storage when the sun shines.

Yes, we have horizontal loops...Make sure your installer provides you a geolink report.

I'll have to go with vertical bore loops here in Central NY - too cold, otherwise. I see that the GeoLink report is a WaterFurnace-derived system estimator - good tip. Thanks.

My German frugality cannot bear to see that money spent so I choose to burn wood instead. I have thousands of dead ash trees in my woods that need cut down and burned anyways.

Mixed Swedish-German heritage here...same issue I have 75 acres, with 45-50 acres wooded. Enough blows down every year in easily accessible areas to give me 3 or more full cords a year, so I'll still be burning a lot of wood too. But I'll likely be doing it in only the colder months of the year and using other methods (e.g., heat pumps) during shoulder seasons and when the sun is shining and I can power it from the PV panels.

I would also recommend getting an Intellistart for your geo.

Definitely in the plans - I'm quite familiar with the surge current during a motor startup. Anyone who has every sent the peak RMS current for a small fridge compressor during startup would be terrified enough to get a motor soft-start for a heat pump....

My second recommendation is to hook the DSH on the geo up to the cheapest 80 gallon hot water tank ( think of that as a battery ) you can buy and then buy a HPHW to make hot water when your geo isn't running.

I thought the DSH would only create usable "warm" water when the heat pump is running in cooling mode - am I wrong? We don't have much need for AC in Central NY, and the 1 or 2 weeks we might need it we would probably use the mini-split or a window AC unit, so I thought the DSH would be of dubious value. In my village house, I do already have a Marathon hot water with an add-on Geyser HPWH - I like it a lot for the dehumidification of the basement. So I'll definitely be doing this in the new place - it's just a question as to whether I pre-heat through my large 500+ gallon buffer tank or through something else.

Wood boiler here. 5 cords per year, no problems. I can also heat with it when the power goes out.

Yeah, if it was just me, that's what I would really like to do - get a nice Frohling boiler. I would enjoy the technology. But I have to look ahead in time and around what would happen if I wasn't there to tend it. Realistically, my wife would not feed a wood boiler with 80 pounds of wood a day, and in 15 more years, I might not want to cut, split, stack, move, etc. 3 or 4 cords of wood every year. With a stove, we could burn as little or as much wood as we wanted, and my wife or I could turn a switch on and run something else when we wanted. If something happened to me, my wife wouldn't have to do a thing.